Rffc 



SCIENTIFIC SIDE-LIGHTS 



513 



are the memorable words which are put into 

 the mouth of Pythagoras by the Roman 

 poet, and they are followed by speculations 

 as to the cause of volcanic vents shifting 

 their positions. Whatever doubts the phi- 

 losopher expresses as to the nature of these 

 causes, it is assumed, as incontrovertible, 

 that the points of eruption will hereafter 

 vary, because they have formerly done so; 

 a principle of reasoning which, as I have 

 endeavored to show in former chapters, has 

 been too much set at naught by some of the 

 earlier schools of geology, which refused to 

 conclude that great revolutions in the 

 earth's surface are now in progress, or that 

 they will take place hereafter, because they 

 have often been repeated in former ages. 

 LYELL Principles of Geology, bk. ii, ch. 22, 

 p. 345. (A., 1854.) 



2518. PAST INHARMONIOUS WITH 

 PRESENT SEEMS REMOTE Thus, when 

 we have lost something we cherished dearly, 

 and the recollection of it brings fruitless 

 longing, we instinctively seek to expel the 

 recollection from our minds. The very feel- 

 ing that what has been can never again be 

 seems to induce this idea of a vast remote- 

 ness of the vanished reality. When, more- 

 over, the lost object was fitted to call forth 

 the emotion of reverence, the impulse to 

 magnify the remoteness of the loss may not 

 improbably be reenforced by the circum- 

 stance that everything belonging to the dis- 

 tant past is fitted on that account to excite 

 a feeling akin to reverence. So, again, any 

 rupture in our mental development may 

 lead us to exaggerate the distance of some 

 past portion of our experience. When we 

 have broken with our former selves, either 

 in the way of worsening or bettering, we 

 tend to project these further into the past. 

 SULLY Illusions, ch. 10, p. 260. (A., 

 1897.) 



2519. PAST, TRIUMPHS OF EVOLU- 

 TION IN THE Nature Always Succeeds The 

 Pledge of What Is To Be. All the other 

 kingdoms of Nature culminated; evolution 

 always attains; always rounds off its work. 

 It spent an eternity over the earth, but fin- 

 ished it. It struggled for millenniums to 

 bring the vegetable kingdom up to the flow- 

 ering plants, and succeeded. In the animal 

 kingdom it never paused until the possi- 

 bilities of organization were exhausted in 

 the mammalia. Kindled by this past, man 

 may surely say, " I shall arrive." The fur- 

 ther evolution must go on, the higher king- 

 dom come first the blade, where we are to- 

 day; then the ear, where we shall be to- 

 morrow; then the full corn in the ear, 

 which awaits our children's children, and 

 which we live to hasten. DRUMMOND As- 

 cent of Man, ch. 10, p. 346. ( J. P., 1900.) 



2520. PATH OF AMAZON SCOOPED 

 FROM A VAST PLAIN Hills Mark Ancient 

 Level. It is delightful to Mr. Agassiz, in 

 returning to this locality, to find that phe- 

 nomena, which were a blank to him on our 



voyage up the river, are perfectly explicable 

 now that he has had an opportunity of 

 studying the geology of the Amazonian Val- 

 ley. When we passed these singular flat- 

 topped hills before, he had no clue to their 

 structure or their age, whether granite, as 

 they have been said to be, or sandstone or 

 limestone; whether primitive, secondary, or 

 tertiary: and their strange form made the 

 problem still more difficult. Now he sees 

 them simply as the remnants of a plain 

 which once filled the whole valley of the 

 Amazons, from the Andes to the Atlantic, 

 from Guiana to Central Brazil. Denuda- 

 tions on a colossal scale, hitherto unknown 

 to geologists, have turned this plain into a 

 labyrinth of noble rivers, leaving only here 

 and there, where the formation has resisted 

 the rush of waters, low mountains and 

 chains of hills to tell what was its thick- 

 ness. AGASSIZ Journey in Brazil, ch. 12, p. 

 374. (H. M. & Co., 1896.) 



2521. PATHWAYS FOR LIGHT 

 THROUGH SOLIDS Magnetism Opens a Way. 

 To the ether the glass is like a sieve, and 

 so is any substance. Light-waves fly in 

 straight lines. The openings through the 

 glass are probably straight, so the light can 

 pass directly through, but the openings 

 through an opaque body are crooked; the 

 molecules overlap in such a way that there 

 is no direct line through the substance, 

 hence the light will either be absorbed or 

 reflected when it strikes upon an opaque 

 body. 



Some idea of what we mean by the over- 

 lapping of molecules may be had by the fol- 

 lowing experiment. Fill a tube with finely 

 pulverized iron filings made into a thin 

 paste. Let the two ends of the tube be 

 stopped with glass heads. Throw a strong 

 beam of light on one end so that the direc- 

 tion of the beam will be in the direction of 

 the length of the tube. Place the tube into 

 a helix (a coil of wire), and pass a current 

 of electricity through the wire of the helix. 

 Now so direct the arrangement that the 

 beam of light strikes upon a screen, and 

 a spot of light will appear on the screen as 

 long as the current is passing; when the 

 current is broken, the spot of light will dis- 

 appear. The magnetism rearranges the par- 

 ticles of the naturally opaque mass of iron 

 filings so that light can pass between them; 

 they are transparent. When the current is 

 taken off, the magnetism disappears, and 

 the particles arrange themselves again in 

 such a way as to shut off the light. The body 

 becomes opaque. ELISHA GRAY Nature's 

 Miracles, vol. ii, ch. 23, p. 191. (F. H. & H., 

 1900.) 



2522. PATIENCE AND EXACTNESS 

 OF SCIENCE Through the precautions, 

 variations, and repetitions observed and 

 executed with the view of rendering its re- 

 sults secure, the separate vessels employed 

 in this inquiry [as to spontaneous genera- 

 tion] have mounted up in two years to 



